1. Field of the Invention
The present invention relates to an abnormality determination device of a fuel property sensor, and a method of determining abnormality of the same.
2. Description of Related Art
For example, Japanese Patent Application Publication No. 2010-256038 (JP 2010-256038 A) discloses a technology regarding abnormality determination of an alcohol concentration sensor that is one of fuel property sensors, in particular, a technology that determines presence of stack abnormality where an output of an alcohol concentration sensor shows a constant value and becomes unable to show a change corresponding to the alcohol concentration. In JP 2010-256038 A, a charge period and a discharge period of a detection electrode of the alcohol concentration sensor are switched between two different periods of a first or a second period. As an output of the alcohol concentration sensor, an output corresponding to an electrostatic capacitance of a detection electrode in each of the first and second periods is detected. In JP 2010-256038 A, when a state where a difference between both outputs is not more than a predetermined value continues, the alcohol concentration sensor is determined to be in a state of stack abnormality.
In JP 2010-256038A, when an ON/OFF of a switch is repeated at a plurality of different frequencies, the detection electrode is charged and discharged at different periods. However, when it is required to switch a plurality of frequencies to detect a fault of a fuel property sensor, due to a circuit for carrying out the switching accurately and the like, a cost regarding the fuel property sensor is considered to increase. Further, characteristics of change of the sensor output in accordance with the periods of charge and discharge vary depending on the component of the fuel. Therefore, when the abnormality determination is performed with the plurality of periods, it is necessary to apply adaptation by considering characteristics of every fuel to each of the plurality of periods, and it is considered that man-hours for adaptation increase.